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[TowerTalk] Coax Question

To: <>
Subject: [TowerTalk] Coax Question
From: "Jim Thomson" <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Wed, 14 Apr 2010 02:16:44 -0700
List-post: <">>
Date: Tue, 13 Apr 2010 21:53:49 -0700
From: jimlux <>
Subject: Re: [TowerTalk] Coax Question

Kipton Moravec wrote:
> On Tue, 2010-04-13 at 07:15 +0000, van wd8aam wrote:
>> In regards to long runs of coax, has any thought EVER been
>> given to RG213 to a remote tuned high power amplifier
>> at the base of the tower.  I've thought about it, and for
>> costs, it might be cost effective.  I'm sure someone has this
>> working for them somewhere.  What do you guru's say to this?
>> van
>> wd8aam

##  it's already been done.. and that was 10 yrs ago ! 
The kicker is... if you have say 3 db of loss back to the
station, then you need an extra 3db of drive power. You 
also LOSE  3 db on RX !    You also require a LONG run of  240 vac
line, to base of tower,   OR a 240-600 vac  xfmr  at the house..
 then  another  600-240vac step down xfmr at base of tower. 

##  getting the power out there is gonna  kill it right there. 
600-240  xfmrs  [can be run either way]   in 5-10 kva 
variety are available surplus.. then  some small ga wire
could be used.  Usually, the xfmr at the far end will have
taps on it.. like 575v.. or 550v etc.... to factor in the V drop,
so u end up getting the full 240 vac... but only under full bore load.
No load, the V will rise > 240vac .  BIG  ga  AL wire between the
2 x xfmr's would work. 

##  Ok, now you need a small, secure, heated building, to put the
xfmr plus 1.5 kw amp, plus any SDR radio, etc. 

## In the final analysis, cheaper to just use BIG coax.  

##  Most telco's in NA, have what's called an "IRG"
[inventory recovery group]... usually now run by contractor's, whose
job it is to store un-used eq.. AND cable.   They sell cheap, to dispose of this
junk, at pennies on the dollar.  A buddy in W7 land  picked up several 
1000' spools of 7/8"  heliax, NEW... for  $116.00 per reel.  The usual deal is,
some proposed cell site  new job/addition gets cancelled, AFTER the eq has 
arrived.  It then all goes to the IRG warehouse.  Meanwhile, the same engineer
orders all new eq  for yet another site !   Most of the contractor's  at the 
various IRG's
wouldn't know  heliax  from a hole in the grnd.  Lot's of other good stuff, like
19" /24"  racks, etc.   You have to be in the right place.. at the right time.. 
snooze, you lose.  If you see  5 x 5'-6' diam reels of coax... and it sez 
on the side of it, snap it up, pay CASH, and get it outa there asap. 

Andrew also makes heliax in corogated AL shield   these days... [ instead of
Cu]   The newer AL stuff still uses a CU  tube in the middle. 

##  Plan B is the catv coax route.  Most of their stuff is  3/4" OD, with a 8 
ga center
conductor. Solid AL sheath, so you need the coring tool, to put the fittings on 
Modified LMR-600  connector's  might also work. 

later... Jim   VE7RF  

>> At 06:04 4/13/2010, you wrote:
>>> On Mon, 12 Apr 2010 21:07:25 -0400, Steve Bagley wrote:
>>>> I am putting up a tower and will need to run about 500 feet of coax.
> I would probably put a Software Defined Radio (and computer) at the base
> of the tower and run Ethernet cable back to the shack. Even with that
> you will need a switch in the middle as Ethernet has length limit of 300
> feet.
> Kip

Use an 802.11 wireless LAN link with directional antennas.  Now all you 
do is run AC power out there.


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